1. Field of the Invention
The present invention relates to the structure of an ink jet recording head for jetting an ink droplet from a nozzle aperture by expanding or contracting a part of a pressure generating chamber communicating with a nozzle aperture by an actuator for flexural oscillation.
2. Related Art
The above ink jet recording head is classified into two types of a piezoelectric vibrator type for mechanically deforming a pressure generating chamber and pressurizing ink and a bubble jet type for providing a heating element in a pressure generating chamber and pressurizing ink by the pressure of bubbles generated by the heat of the heating element. The piezoelectric vibrator type of recording head is further classified into two types of a first recording head using a piezoelectric vibrator displaced axially and a second recording head using a piezoelectric vibrator for flexural displacement.
Although the first recording head enables high speed driving and recording in high density, it has a problem that the number of manufacturing processes is many because cutting is required for working its piezoelectric vibrator and three-dimensional assembly is required when a piezoelectric vibrator is fixed to a pressure generating chamber. In the meantime, although the second recording head is characterized in that a piezoelectric vibrator can be integrated with an elastic film constituting a pressure generating chamber by baking because the piezoelectric vibrator is filmy and the manufacturing process can be simplified, it has a problem that the width of the pressure generating chamber is increased and the density of an array is deteriorated because large area enough to enable flexural oscillation is required.
To solve such problems which the recording heads utilizing flexural oscillation have, an ink jet recording head provided with a passage formed substrate in which a pressure generating chamber, an ink supply port and a common ink chamber are formed by anisotropically etching a silicon monocrystalline substrate with a lattice plane (110) and a nozzle plate in which plural nozzle apertures communicating with a pressure generating chamber are formed wherein the other face of the passage formed substrate is constituted as a membrane which can be elastically deformed by a silicon oxide is proposed in Japanese published patent application No. H5-504740 for example.
According to the above ink jet recording head, as a driving part is formed by forming a piezoelectric material film in the area opposite to a pressure generating chamber of a membrane by a film forming method and the recording head can be constituted by etching and forming a film, the multiple recording heads with high printing density can be uniformly and simultaneously manufactured.
However, there are problems with the above structure in which a film to be a piezoelectric vibrator is formed using a silicon monocrystalline substrate to be improved to further enhance the quality of printing and to reduce the manufacturing cost.
As for a first problem, as a silicon monocrystalline substrate is thin and fragile, some reinforcement against impact and vibration is required.
As for a second problem, the coefficient of linear expansion of a silicon monocrystalline substrate is approximately 3.times.10.sup.-6 /.degree. C. and very small, compared with the coefficient of linear expansion of general metal and resin. Therefore, if metal and resin respectively with the large coefficient of linear expansion are used for the other head component when a silicon monocrystalline substrate is assembled by sticking an ink passage component and the other head component such as a nozzle plate together, tensile stress or compressive stress is applied to the silicon monocrystalline substrate due to a difference in the quantity of expansion or contraction between both as temperature changes. Stress applied to the silicon monocrystalline substrate particularly sensitively has an effect upon a thin film part and substantially changes the rigidity of an elastic film, therefore, pressure applied to a pressure generating chamber by a piezoelectric element and the vibrational characteristic of the pressure generating chamber are changed and as a result, the jetting of an ink droplet is unstable. The bonded body is warped due to the difference in expansion or contraction between the above-noted substrate and other componet and the failure of bonding is caused when a recording head is built in a frame and others in a succeeding process.
Next, a third problem will be described. A substrate in regular size (hereinafter called a wafer) normally such as four and eight inches is used for the silicon monocrystalline substrate. No matter how many pressure generating chambers and piezoelectric elements of recording heads are formed by one wafer, man-hours, time and material are unchanged. In addition, the manufacturing cost of a pressure generating chamber and a piezoelectric element accounts for most of the cost of a recording head. That is, the greater the number is of recording heads manufactured of one particular wafer, the lower the cost of one recording head can be. It remarkably reduces the number of recording heads manufactured of one wafer that a passage except a pressure generating chamber, particularly a common ink chamber requiring much area is formed in a silicon monocrystalline substrate as in the above prior example and as a result, the cost of a recording head is increased.